What's the difference between fibromyalgia, tendonitis and arthritis?

Not much: Arthritis is a result of cartilage breakdown causing inflammation, pain and stiffness in the joints. Tendonitis is an injury and inflammation in the tendons. It can happen anywhere in the tendon, but typically it manifests where the muscles and tendons meet. The cause of fibromyalgia is currently unknown.Symptoms of fibromyalgia are chronic widespread pain, fatigue.

Pain Syndromes: While arthritis is a pain condition of the joints often related to injury and inflammation, tendonitis is usually an injury to the tendons. Fibromyalgia is a pain but it is due to lack of energy molecules reaching the muscle tissue, causing cramping of the tissues and therefore pain. It needs to be treated entirely differently than the other two conditions.